1. Field of the Invention
This invention relates to electronic circuits connected to power supplies which produce noisy outputs and more particularly to circuits for reducing the noise introduced by the power supply.
2. Description of Related Art
To some degree, almost all electronic circuits are susceptible to noise on their power supply or ground input lines.
FIG. 1 shows a typical prior art system 10 including a supply voltage VDD input connected through a terminal via line 60 and line 63 to the power supply input of a typical VDD Noise Sensitive Circuit (NSC) 11. The NSC 11 is also connected by lines 66 and 64 to ground (reference potential) connection of the VDD power supply to complete to the power supply circuit connection as will be well understood by those skilled in the art. Unfortunately, the power supply voltage includes a noise signal NS which is an unwanted component included with the direct current voltage VDD. A control circuit 12 is also included in system 10. The control circuit 12 is connected to receive power from the power supply through the lines 62 and 60. The ground of the control circuit 62 is connected by lines 65 and 64 to ground (reference potential) to complete the connections to the power supply. The control circuit provides control signals on output line 52 connected to an input of the NSC 11.
The typical VDD noise sensitive circuit 11 is sensitive to an unwanted input noise signal NS which is representative of certain frequencies included with the Direct Current (DC) power supply voltage VDD on line 60 which cause an unacceptable operational problem for the NSC 11. For example, in FIG. 1, the output signal OS is shown on the output line 9 from NSC 11. Thus the output signal OS from the NSC 11 is noisy and in many applications, the noise must be substantially reduced in amplitude for the output signal OS to meet specifications.
In summary the noise NS received by control circuit 12 and noise sensitive circuit 11 has an unwanted harmful effect on the typical noise sensitive circuit 11 producing an output noise signal OS along with the output signal from circuit 11 on line 9.
FIG. 2 is a modification of the electrical schematic diagram of FIG. 1 which shows a prior art method for combating the noise sensitivity problem by adding a decoupling capacitor 15 across to the power supply to reduce the noise output signal OSxe2x80x2 on output line 9. The capacitor 15 can filter out the noise by providing an effective short circuit for the Alternating Current (AC) component of the noise. The upper plate of the capacitor 15 is connected by line 61 to line 60 to the power supply. The lower plate of capacitor 15 is connected by line 67 via to line 64 to ground completing the power supply capacitor circuit. However, when the circuit of FIG. 2 is embodied on a small microchip the decoupling capacitor 15 can consume too much area on the surface of the small microchip.
FIG. 3 is a modification of the electrical schematic diagram of FIG. 2 which shows a prior art method in which there are dual output lines 52xe2x80x2/52xe2x80x3 in place of the single output line 52 in FIG. 2.
Other prior art approaches to combating the noise sensitivity problem require signal processing or filtering of the output of the affected circuit, which can be very complicated and costly.
U.S. Pat. No. 4,630,104 of Nakagaki et al for xe2x80x9cCircuit Arrangement for Removing Noise of a Color Video Signalxe2x80x9d describes apparatus for color video signal processing to separate noise in a color video signal from the output, then subtract it from the color video signal output. This reference is not directed to solving the problem of power supply noise. A luminance signal and a chroma signal of a color video signal are processed to generate a first signal and a second signal, respectively. The first signal indicates the contour line of images represented by the video signal. The second signal includes noise included in the chroma signal and a signal component having an amplitude substantially equal to the peak to peak value of the noise. The first and second signals are fed to either a switching circuit or a multiplier so that a resultant output signal having only the noise is obtained. The noise components are then subtracted, by way of a subtractor, from the chroma signal so that a chroma signal having no noise will be obtained.
U.S. Pat. No. 4,475,215 of Gutleber entitled xe2x80x9cPulse Interference Cancelling System for Spread Spectrum Signals Utilizing Active Coherent Detectionxe2x80x9d describes a pulse interference canceling system for spread spectrum signals utilized in a digital noise coded communications system. A noise coded signal that is phase shifted by 180xc2x0 is added to the original to cancel noise and to recover the coded signal. The system includes first and second noise coded signal channels located in a noise coded signal receiver which also includes a demultiplexer for providing a pair of received noise coded signals which were initially generated, multiplexed and transmitted to the receiver. First and second coherent detectors are coupled to both signal channels, the first being directly coupled thereto so that no signal delay exists. The second is coupled to the two signal channels with respective first and second variable time delay circuits having a delay substantially equal to the bit width of each digital code as well as a vernier delay which is adapted to delay the phase of any received pulse interference in the respective channel so that it is exactly 180xc2x0 out of phase with the same undelayed pulse interference. Signal summing means are coupled to the outputs of the two coherent detectors which operate to completely cancel the interference pulse signal while leaving the desired noise coded signal at its peak amplitude.
U.S. Pat. No. 6,052,420 of Yeap et al. entitled xe2x80x9cAdaptive Multiple Sub-band Common-mode RFI Suppressionxe2x80x9d uses a common mode signal to estimate noise in narrow frequency band. The estimate is subtracted from the original signal. A noise suppression circuit for a two wire communications channel comprising a hybrid device, e.g. a hybrid transformer or circuit, which provides a differential mode signal corresponding to a differential signal received from the channel. A summing device extracts from the channel wires a common mode signal that it supplies to a noise estimation unit that derives a common mode signal as an estimate of a noise level in a frequency band having a bandwidth narrower than an operating channel bandwidth. The noise estimation unit adjusts the amplitude of the noise estimate to correspond to the residual noise in the differential mode signal and subtracts it from the differential mode signal to produce a noise-suppressed output signal. A noise detection and control unit scans the operating band, identifies a frequency band having a highest noise level, and sets the noise estimation unit to the detected noisy band. The noise estimation unit suppresses the noise in that band. Preferably, the noise estimation unit comprises several channels, with a tunable filter, a phase shifter and an amplifier, and the noise detection and control unit sets the channels, in succession, to different frequency bands in descending order of noise level. The noise detection and control unit may cross-correlate the common mode signal and the noise-suppressed output signal and adjust the amplification of the noise estimation signal to reduce residual differential mode noise towards zero.
U.S. Pat. No. 6,061,456 of Andrea entitled xe2x80x9cNoise Cancellation Apparatusxe2x80x9d discloses a transducer for an acoustic noise cancellation apparatus for reducing background noise using microphones and amplifiers. The transducer includes a housing with first microphone for receiving a first acoustic sound, composed mainly of speech and background noise, that converts the first acoustic sound to a first signal. A second microphone is arranged at an angle, close to the first microphone to receive a second acoustic sound, composed mainly of the background noise, that converts the second acoustic sound to a second signal. The first and second microphones are connected to a differential amplifier of the noise cancellation apparatus to obtain a signal mainly representing speech. The amplifier is receives acoustic sounds from each microphone and has a first terminal and a second terminal. The second terminal is grounded. The transducer receives and amplifies an AC signal representative of the audio input from each microphone; and filters out the amplified AC signal from the DC signal. The DC signal powers the amplifier. A method for calibrating an active noise reduction apparatus includes use of a housing having a speaker to produce an acoustic anti-noise signal in the housing. A microphone detects an external noise signal, and amplitude adjustment calibrates the acoustic anti-noise signal creating a quiet zone in the housing for operation with an independent electrical assembly. The apparatus is calibrated separately from the electrical assembly. The method includes the steps of: inputting the external noise signal received by the microphone to produce an anti-noise signal. The anti-noise signal is transmitted to the speaker with an equal gain and an opposite phase response from the external noise signal detected by the microphone. The gain and phase response of the anti-noise signal are balanced by the amplitude adjustment located in the noise reduction apparatus to match the gain and phase response of the external noise signal to yield a theoretical zero in the quiet zone.
U.S. Pat. No. 5,907,624 of Taxidea entitled xe2x80x9cNoise Canceler Capable of Switching Noise Canceling Characteristicsxe2x80x9d describes an acoustic noise canceler which switches noise canceling characteristic on detecting narrow band noise, and which cancels narrow band noise adequately. The noise canceler selects an output signal with a particular noise canceling characteristic, depending on whether or not a speech signal contained in an input acoustic signal is voiced. Also, the noise canceler adaptively changes, for an acoustic signal containing voiced sound, a window function that regulates the depth of a valley of an attenuation characteristic meant for the acoustic signal. The noise canceler improves an output signal with respect to the auditory sense and sound quality without regard to narrow band noise.
It is an object of this invention to diminish the effects of noise within a certain bandwidth by converting the noise to a control current that is fed into the affected circuit with an opposite polarity from the polarity of the noise.
In accordance with this invention, apparatus for compensating for power supply noise comprises a noise compensation amplifier with a power supply input for connection to a power supply. The amplifier provides an instantaneous amplified signal in response to power supply noise with an opposite polarity from the power supply noise. The noise compensation amplifier provides the noise sensitive circuit with a compensated power supply signal which enables it to produce a reduction in the amplitude of the noise signal at the output thereof.
Preferably, the amplifier includes a differential pair of coupled transistor circuits including a leading transistor circuit and a lagging transistor circuit.
Preferably, the leading and lagging transistor circuits have source-drain circuits connected in parallel to the source-drain circuit of a constant current transistor, whereby the leading and lagging transistor circuits share a common current as a function of voltages on the leading node connected to the gate of the leading transistor and a lagging node connected to the gate of the lagging transistor.
Preferably, the differential pair of coupled transistor circuits each have the source/drain circuits thereof connected in series with a transistor source/drain circuit connected to the power supply input; or the differential pair of coupled transistor circuits each have the source/drain circuit thereof connected in series with a resistor connected to the power supply input.
Preferably the amplifier includes a differential pair of coupled transistor circuits including a leading transistor circuit and a lagging transistor circuit the leading transistor circuit includes a first FET transistor having leading node connected to both and the gate electrode thereof and a resistive circuit, and the lagging transistor circuit includes and a lagging FET transistor having a lagging node connected to both the gate electrode thereof and the resistive and capacitive elements.
In accordance with another aspect of this invention, apparatus for compensating for power supply noise comprises a noise compensation amplifier with a power supply input and a reference potential input for connection to a power supply. The amplifier includes a differential amplifier circuit for providing an instantaneous amplified signal in response to power supply noise, and the amplifier produces an output signal with an instantaneous opposite polarity from the power supply noise. Thus, a noise sensitive circuit connected to the noise compensation amplifier has a compensated power supply signal which enables it to produce a reduction in the amplitude of the noise signal at the output thereof.
Preferably, the differential pair of coupled transistor circuits each have the source/drain circuits thereof connected in series with a transistor having the source/drain circuit thereof connected to the power supply input or the differential pair of coupled transistor circuits each have the source/drain circuit thereof connected in series with a resistor connected to the power supply input.
Preferably, and the differential amplifier circuit includes a differential pair of coupled transistor circuits including a leading transistor circuit and a lagging transistor circuit.
In accordance with still another aspect of this invention, apparatus for compensating for power supply noise comprises a noise compensation amplifier with a power supply input and a reference potential input for connection to a power supply. The amplifier includes a differential amplifier circuit for providing an instantaneous amplified signal in response to power supply noise. The amplifier produces an output signal with an instantaneous opposite polarity from the power supply noise. The differential amplifier circuit includes a differential pair of coupled transistor circuits including a leading transistor circuit and a lagging transistor circuit. The leading and lagging transistor circuits have source-drain circuits connected in parallel to the source-drain circuit of a constant current transistor. A current reference constant current source connected to a set of transistors with gate electrodes connected together and source/drain circuits connected to the ground with the gate electrodes connected to the source/drain circuit of one of the set of transistor to provide constant current in the source/drain circuits to the ground circuit. Thus the leading and lagging transistor circuits share a common current as a function of voltages on the leading node connected to the gate of the leading transistor and a lagging node connected to the gate of the lagging transistor and the noise sensitive circuit connected to the noise compensation amplifier has a compensated power supply signal which enables it to produce a reduction in the amplitude of the noise signal at the output thereof.